On Tue, Nov 7, 2017 at 11:32 AM, Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Mon, Nov 06, 2017 at 04:54:54PM -0500, Emilio G. Cota wrote:
>> On Mon, Nov 06, 2017 at 12:10:22 -0200, Eduardo Habkost wrote:
>> > On Fri, Nov 03, 2017 at 06:24:07PM -0400, Emilio G. Cota wrote:
>> > > /**
>> > > * MachineClass:
>> > > * @max_cpus: maximum number of CPUs supported. Default: 1
>> > > + * @force_max_cpus: if set, force the global max_cpus to match @max_cpus
>> > > * @min_cpus: minimum number of CPUs supported. Default: 1
>> > > * @default_cpus: number of CPUs instantiated if none are specified.
>> > > Default: 1
>> > > * @get_hotplug_handler: this function is called during bus-less
>> >
>> > If we have a field containing the default value for smp_cpus
>> > (default_cpus), what about a default_max_cpus field for the
>> > default value of max_cpus? This could make the rules a bit
>> > easier to follow.
>> >
>> > (But I wonder if there's a way we can do this without introducing
>> > another MachineClass field and making the initialization code
>> > more complex.)
>>
>> I don't think the rules are too hard to follow, since they're trivial
>> for most machines because the defaults are reasonable (i.e. they
>> only set max_cpus, and everything else is set to 1). Some machines
>> though are tricky in what can and cannot support, e.g. the Xilinx
>> ones we've been dealing with in this thread.
>>
>> wrt .default_max_cpus instead of .force_max_cpus: it lets users
>> shoot themselves in the foot, so I wouldn't go this route.
>> For instance, what do we do if the user passes maxcpus < default_max_cpus?
>> max_cpus would be set to maxcpus, yet they could still pass the
>> -global override that instantiates two extra CPUs, and at that point
>> we'd fail (in TCG) without providing a meaningful error.
>>
>> We could increase maxcpus to default_max_cpus, but at that point
>> default_max_cpus becomes the same thing as force_max_cpus (!).
>>
>> An alternative I've come up with is to have a field that specifies how
>> many CPUs could be created in addition to those specified in max_cpus
>> (in the Xilinx case these would be the RPUs). Patch below.
>>
>> > The fact that MachineClass::max_cpus and the 'max_cpus' globals
>> > have completely different meanings makes this confusing enough.
>> > Maybe we should rename the 'max_cpus' global variable to
>> > 'max_hotplug_cpus'.
>>
>> I have no trouble with their different meanings, although I admit
>> I am now quite well acquainted with this code so my bias is strong :-)
>>
>> Thanks,
>>
>> Emilio
>>
>> ---8<---
>>
>> Subject: [PATCH] hw: add .{additional_max,min,default}_cpus fields to
>> machine_class
>>
>> max_cpus needs to be an upper bound on the number of vCPUs
>> initialized; otherwise TCG region initialization breaks.
>>
>> Some boards initialize a hard-coded number of vCPUs, which is not
>> captured by the global max_cpus. Fix it by adding the .min_cpus
>> field to machine_class.
>>
>> A subset of those boards can also instantiate additional vCPUs
>> beyond what is specified in -smp, e.g. via -global overrides. To
>> ensure that max_cpus remains an upper bound on the number of vCPUs
>> that can be instantiated, we also add the .additional_max_cpus field
>> to machine_class.
>
> Setting max_cpus > smp_cpus is supposed to be useful only for CPU
> hotplug, and this doesn't seem to be the case here. I would
> prefer to make the CPU creation code not care about max_cpus at
> all unless it is dealing with CPU hotplug, but this would require
> auditing existing code that could be allocating data structures
> based on max_cpus.
>
> In either case, it looks like the series sent by Alistair:
> Subject: [PATCH v1 0/2] Xilinx ZCU102 fixes for 2.11
> makes max_additional_cpus unnecessary, doesn't it?
Yes, it doesn't need the max_additional_cpus at all.
I would still like to see the default_cpus in, as I think that is
really useful. Otherwise 2.10 has 4 A53s and 2.11 has 1 A53 by default
which I think is confusing.
Thanks,
Alistair
>
>
>>
>> This commit also changes some user-facing behaviour: we now die if
>> -smp is below this hard-coded vCPU minimum instead of silently
>> ignoring the passed -smp value (sometimes announcing this by printing
>> a warning). However, the introduction of .default_cpus lessens the
>> likelihood that users will notice this: if -smp isn't set, we now
>> assign the value in .default_cpus to both smp_cpus and max_cpus. IOW,
>> if a user does not set -smp, they always get a correct number of vCPUs.
>>
>> This change fixes 3468b59 ("tcg: enable multiple TCG contexts in
>> softmmu", 2017-10-24), which broke TCG initialization for some
>> ARM boards.
>>
>> Fixes: 3468b59e18b179bc63c7ce934de912dfa9596122
>> Reported-by: Thomas Huth <th...@redhat.com>
>> Suggested-by: Peter Maydell <peter.mayd...@linaro.org>
>> Signed-off-by: Emilio G. Cota <c...@braap.org>
>> ---
>> hw/arm/exynos4_boards.c | 12 ++++--------
>> hw/arm/raspi.c | 2 ++
>> hw/arm/xlnx-zcu102.c | 9 ++++++++-
>> include/hw/boards.h | 10 ++++++++++
>> vl.c | 38 +++++++++++++++++++++++++++++++++++---
>> 5 files changed, 59 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/arm/exynos4_boards.c b/hw/arm/exynos4_boards.c
>> index f1441ec..750162c 100644
>> --- a/hw/arm/exynos4_boards.c
>> +++ b/hw/arm/exynos4_boards.c
>> @@ -27,7 +27,6 @@
>> #include "qemu-common.h"
>> #include "cpu.h"
>> #include "sysemu/sysemu.h"
>> -#include "sysemu/qtest.h"
>> #include "hw/sysbus.h"
>> #include "net/net.h"
>> #include "hw/arm/arm.h"
>> @@ -129,13 +128,6 @@ exynos4_boards_init_common(MachineState *machine,
>> Exynos4BoardType board_type)
>> {
>> Exynos4BoardState *s = g_new(Exynos4BoardState, 1);
>> - MachineClass *mc = MACHINE_GET_CLASS(machine);
>> -
>> - if (smp_cpus != EXYNOS4210_NCPUS && !qtest_enabled()) {
>> - error_report("%s board supports only %d CPU cores, ignoring
>> smp_cpus"
>> - " value",
>> - mc->name, EXYNOS4210_NCPUS);
>> - }
>>
>> exynos4_board_binfo.ram_size = exynos4_board_ram_size[board_type];
>> exynos4_board_binfo.board_id = exynos4_board_id[board_type];
>> @@ -189,6 +181,8 @@ static void nuri_class_init(ObjectClass *oc, void *data)
>> mc->desc = "Samsung NURI board (Exynos4210)";
>> mc->init = nuri_init;
>> mc->max_cpus = EXYNOS4210_NCPUS;
>> + mc->min_cpus = EXYNOS4210_NCPUS;
>> + mc->default_cpus = EXYNOS4210_NCPUS;
>> mc->ignore_memory_transaction_failures = true;
>> }
>>
>> @@ -205,6 +199,8 @@ static void smdkc210_class_init(ObjectClass *oc, void
>> *data)
>> mc->desc = "Samsung SMDKC210 board (Exynos4210)";
>> mc->init = smdkc210_init;
>> mc->max_cpus = EXYNOS4210_NCPUS;
>> + mc->min_cpus = EXYNOS4210_NCPUS;
>> + mc->default_cpus = EXYNOS4210_NCPUS;
>> mc->ignore_memory_transaction_failures = true;
>> }
>>
>> diff --git a/hw/arm/raspi.c b/hw/arm/raspi.c
>> index 5941c9f..cd5fa8c 100644
>> --- a/hw/arm/raspi.c
>> +++ b/hw/arm/raspi.c
>> @@ -167,6 +167,8 @@ static void raspi2_machine_init(MachineClass *mc)
>> mc->no_floppy = 1;
>> mc->no_cdrom = 1;
>> mc->max_cpus = BCM2836_NCPUS;
>> + mc->min_cpus = BCM2836_NCPUS;
>> + mc->default_cpus = BCM2836_NCPUS;
>> mc->default_ram_size = 1024 * 1024 * 1024;
>> mc->ignore_memory_transaction_failures = true;
>> };
>> diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
>> index e2d15a1..0f1837e 100644
>> --- a/hw/arm/xlnx-zcu102.c
>> +++ b/hw/arm/xlnx-zcu102.c
>> @@ -185,6 +185,10 @@ static void xlnx_ep108_machine_class_init(ObjectClass
>> *oc, void *data)
>> mc->block_default_type = IF_IDE;
>> mc->units_per_default_bus = 1;
>> mc->ignore_memory_transaction_failures = true;
>> + mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> + mc->max_additional_cpus = XLNX_ZYNQMP_NUM_RPU_CPUS;
>> + mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> + mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> }
>>
>> static const TypeInfo xlnx_ep108_machine_init_typeinfo = {
>> @@ -240,7 +244,10 @@ static void xlnx_zcu102_machine_class_init(ObjectClass
>> *oc, void *data)
>> mc->block_default_type = IF_IDE;
>> mc->units_per_default_bus = 1;
>> mc->ignore_memory_transaction_failures = true;
>> - mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
>> + mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> + mc->max_additional_cpus = XLNX_ZYNQMP_NUM_RPU_CPUS;
>> + mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> + mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
>> }
>>
>> static const TypeInfo xlnx_zcu102_machine_init_typeinfo = {
>> diff --git a/include/hw/boards.h b/include/hw/boards.h
>> index 191a5b3..be582dd 100644
>> --- a/include/hw/boards.h
>> +++ b/include/hw/boards.h
>> @@ -102,6 +102,13 @@ typedef struct {
>>
>> /**
>> * MachineClass:
>> + * @max_cpus: maximum number of CPUs supported. Default: 1
>> + * @max_additional_cpus: # of CPUs that can be instantiated in addition to
>> those
>> + * instantiated with -smp. For instance, if a machine has 4 main CPUs
>> and 2
>> + * optional CPUs (e.g. instantiated via -global overrides), then
>> @max_cpus
>> + * and @max_additional_cpus will be set to 4 and 2, respectively.
>> Default: 0
>> + * @min_cpus: minimum number of CPUs supported. Default: 1
>> + * @default_cpus: number of CPUs instantiated if none are specified.
>> Default: 1
>> * @get_hotplug_handler: this function is called during bus-less
>> * device hotplug. If defined it returns pointer to an instance
>> * of HotplugHandler object, which handles hotplug operation
>> @@ -167,6 +174,9 @@ struct MachineClass {
>> BlockInterfaceType block_default_type;
>> int units_per_default_bus;
>> int max_cpus;
>> + int max_additional_cpus;
>> + int min_cpus;
>> + int default_cpus;
>> unsigned int no_serial:1,
>> no_parallel:1,
>> use_virtcon:1,
>> diff --git a/vl.c b/vl.c
>> index ec29909..e3ee36e 100644
>> --- a/vl.c
>> +++ b/vl.c
>> @@ -160,8 +160,8 @@ Chardev *virtcon_hds[MAX_VIRTIO_CONSOLES];
>> Chardev *sclp_hds[MAX_SCLP_CONSOLES];
>> int win2k_install_hack = 0;
>> int singlestep = 0;
>> -int smp_cpus = 1;
>> -unsigned int max_cpus = 1;
>> +int smp_cpus;
>> +unsigned int max_cpus;
>> int smp_cores = 1;
>> int smp_threads = 1;
>> int acpi_enabled = 1;
>> @@ -4330,12 +4330,44 @@ int main(int argc, char **argv, char **envp)
>> smp_parse(qemu_opts_find(qemu_find_opts("smp-opts"), NULL));
>>
>> machine_class->max_cpus = machine_class->max_cpus ?: 1; /* Default to
>> UP */
>> + machine_class->min_cpus = machine_class->min_cpus ?: 1;
>> + machine_class->default_cpus = machine_class->default_cpus ?: 1;
>> +
>> + /* if -smp is not set, default to mc->default_cpus */
>> + if (!smp_cpus) {
>> + smp_cpus = machine_class->default_cpus;
>> + max_cpus = machine_class->default_cpus;
>> + }
>> +
>> + /* sanity-check smp_cpus and max_cpus */
>> + if (smp_cpus < machine_class->min_cpus) {
>> + error_report("Invalid SMP CPUs %d. The min CPUs "
>> + "supported by machine '%s' is %d", smp_cpus,
>> + machine_class->name, machine_class->min_cpus);
>> + exit(1);
>> + }
>> if (max_cpus > machine_class->max_cpus) {
>> - error_report("Invalid SMP CPUs %d. The max CPUs "
>> + error_report("Invalid max SMP CPUs %d. The max CPUs "
>> "supported by machine '%s' is %d", max_cpus,
>> machine_class->name, machine_class->max_cpus);
>> exit(1);
>> }
>> + if (max_cpus < machine_class->min_cpus) {
>> + error_report("Invalid max SMP CPUs %d. The min CPUs "
>> + "supported by machine '%s' is %d", max_cpus,
>> + machine_class->name, machine_class->min_cpus);
>> + exit(1);
>> + }
>> +
>> + /*
>> + * Some boards can instantiate additional CPUs, e.g. by overriding
>> + * device params via -global arguments. Update max_cpus so that
>> + * we are sure to have an upper bound on the maximum number of
>> + * vCPUs that might be instantiated.
>> + */
>> + if (machine_class->max_additional_cpus) {
>> + max_cpus += machine_class->max_additional_cpus;
>> + }
>>
>> /*
>> * Get the default machine options from the machine if it is not already
>> --
>> 2.7.4
>>
>
> --
> Eduardo
>
